ECMA-334: 11. Types

Microsoft .NET Framework, ASP.NET, Visual C# (CSharp, C Sharp, C-Sharp) Developer Training, Visual Studio

11. Types

The types of the C# language are divided into three main categories: Value types, reference types, and type-parameter types.

type:

value-type

reference-type

type-parameter

Type parameters are part of generics, and are discussed in §25.1.1. A fourth category of types, pointers, is available only in unsafe code. This is discussed further in §27.2.

Value types differ from reference types in that variables of the value types directly contain their data, whereas variables of the reference types store references to their data, the latter being known as objects. With reference types, it is possible for two variables to reference the same object, and thus possible for operations on one variable to affect the object referenced by the other variable. With value types, the variables each have their own copy of the data, and it is not possible for operations on one to affect the other. [Note: When a variable is a ref or out parameter, it does not have its own storage but references the storage of another variable. In this case, the ref or out variable is effectively an alias for another variable and not a distinct variable. end note]

C#’s type system is unified such that a value of any type can be treated as an object. Every type in C# directly or indirectly derives from the object class type, and object is the ultimate base class of all types. Values of reference types are treated as objects simply by viewing the values as type object. Values of value types are treated as objects by performing boxing and unboxing operations (§11.3).